Ordovician ferrosilicic magmas: Experimental evidence for ultrahigh temperatures affecting a metagreywacke source |
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| Institution: | 1. V.S. Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the RAS, 3, Ac. Koptyuga Ave., Novosibirsk 630090, Russian Federation;2. Novosibirsk State University, Pirogova St. 2, Novosibirsk 630090, Russian Federation;3. JV Tairus, 3, Ac. Koptyuga Ave., Novosibirsk 630090, Russia;1. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia;2. Shmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow 123995, Russia;1. V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Koptyuga ave. 3, Novosibirsk 630090, Russia;2. Institute of Petrology and Structural Geology, Charles University, Prague 12843, Czech Republic;3. Laboratories of the Geological Institutes, Charles University, Prague 12843, Czech Republic;4. Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University, Prague 12843, Czech Republic;1. Institut für Mineralogie und Kristallographie, Universität Wien, A - 1090 Wien, Austria;2. Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk 664033, Russia;3. Department of Imaging and Applied Physics, Curtin University of Technology, Perth, WA 6102, Australia;1. Instituto de Geociências, Universidade Federal do Rio Grande do SUL (UFRGS), 91.501-970 Porto Alegre, RS, Brazil;2. Departamento Nacional de Produção Mineral, 88.020-180 Florianópolis, SC, Brazil;3. Laboratório Central de Microscopia Eletrônica (LCME-UFSC), 88.040-900 Florianópolis, SC, Brazil;4. Facultat de Geologia, Universitat de Barcelona (UB), 88028, Barcelona, Spain;5. Instituto de Física, UFRGS, 91-501-970 Porto Alegre, RS, Brazil;1. School of Geosciences, University of Sydney, Australia;2. Geology Department, Lakehead University, 955 Oliver Rd, Thunder Bay, Ontario P7B 5E1, Canada;3. Laboratório de Geologia Isotópica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil |
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| Abstract: | Peculiar magmatic rocks were erupted and emplaced at depth at the margin of the Gondwana supercontinent during the Cambro-Ordovician transition. These rocks are characterized by high contents in silica and iron but they do not have equivalents in the high-silica members of the calc-alkaline series. They have particular geochemical signatures, with Al saturation index, ASI > 1, FeO > 2.5 wt.%, MgO > 0.8 wt.% for very low contents in calcium (CaO < 2.0 wt.%), supporting a derivation from near-total melting (> 80 vol.% melt) of metagreywackes. The results from inverse experiments indicate that the most plausible conditions are within the range 1000 °C (excess water) and 1100–1200 °C (subsaturated and dry) at pressures of 1.5 to 2.0 GPa. A tectonic scenario implying melting of subducted sediments within an ascending mantle-wedge plume is suggested for the generation of primary ferrosilicic melts at the Gondwana continental margin during Upper Cambrian to Lower Ordovician times. |
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